Transfer of AZO dyes

ABSTRACT

Azo dyes are transferred from a substrate to a plastic-coated paper by diffusion with the aid of a thermal printing head, these azo dyes having the formula ##STR1## where R 1  and R 2  are each independently of the other hydrogen, substituted or unsubstituted alkyl or substituted or unsubstituted phenyl, 
     R 3  is hydrogen, alkyl, alkoxy or substituted or unsubstituted alkanoyl- or benzoyl-amino, 
     R 4  is hydrogen, chlorine, alkyl, alkoxy, alkylthio or substituted or unsubstituted phenyl and 
     R 5  is cyano, substituted or unsubstituted alkoxy- or phenoxy-carbonyl or substituted or unsubstituted mono- or di-alkyl- or -phenyl-carbamoyl.

The present invention relates to a novel process for transferring azo dyes having a thiophene-based diazo component from a substrate to a plastic-coated paper with the aid of a thermal printing head.

In thermotransfer printing processes, a transfer sheet which contains a thermally transferable dye in one or more binders with or without suitable assistants on a substrate is heated from the back with a thermal printing head in short heat pulses (duration: fractions of a second), as a result of which the dye migrates out of the transfer sheet and diffuses into the surface coating of a receiving medium. The essential advantage of this process is that control of the amount of dye to be transferred (and hence of the color gradation) is easily possible by adjusting the energy to be supplied to the thermal printing head.

In general, color recording is carried out using the three subtractive primaries yellow, magenta and cyan (and in certain cases black). To facilitate optimal color recording, the dyes must have the following properties:

i) ready thermal transferability,

ii) low migration tendency within or on the surface coating of the receiving medium at room temperature,

iii) high thermal and photochemical stability and resistance to moisture and chemical substances,

iv) suitable hues for subtractive color mixing,

v) a high molar adsorption coefficient,

vi) resistance to crystallization in the course of storage of the transfer sheet and

vii) ready industrial accessibility.

Requirements i), iii), vii) and in particular iv) and v) are from experience particularly difficult to meet in the case of cyan dyes.

For this reason most of the known cyan dyes used for thermal transfer printing do not meet the required range of properties.

There is prior art concerning dyes used in thermotransfer printing processes. For instance, EP-A-216,483 and EP-A-258,856 describe azo dyes from thiophene-based diazo components and aniline-based coupling components.

Furthermore, EP-A-218,937 describes thiophene- and aniline-based disazo dyes for this purpose.

It is an object of the present invention to provide a process for the transfer of dyes where the dyes should ideally meet all the abovementioned requirements i) to vii).

We have found that this object is achieved in an advantageous manner by transferring azo dyes from a substrate to a plastic-coated paper by diffusion with the aid of a thermal printing head on using a substrate on which there are one or more azo dyes of the formula I ##STR2## where R¹ and R² are identical or different and each is independently of the other alkyl, alkanoyloxyalkyl, alkoxycarbonyloxyalkyl or alkoxycarbonylalkyl, which each may have up to 20 carbon atoms and be substituted by phenyl, C₁ -C₄ -alkylphenyl, C₁ -C₄ -alkoxyphenyl, benzoyloxy, C₁ -C₄ -alkylbenzyloxy, C₁ -C₄ -alkoxybenzyloxy, halogen, hydroxyl or cyano, or are each hydrogen, unsubstituted or C₁ -C₂₀ -alkoxy- or halogen-substituted phenyl, unsubstituted or C₁ -C₂₀ -alkyl-, C₁ -C₂₀ -alkoxy- or halogen-substituted benzyl or a radical of the formula II ##STR3## where Y is C₂ -C₆ -alkylene,

m is 1, 2, 3, 4, 5 or 6 and

R⁶ is C₁ -C₄ -alkyl or unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl,

R³ is hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy or --NH--CO--R¹, where R¹ is as defined above,

R⁴ is hydrogen, chlorine, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, C₁ -C₄ -alkylthio or unsubstituted or C₁ -C₄ -alkyl-, C₁ -C₄ -alkoxy- or halogen-substituted phenyl and

R⁵ is cyano or --CO--OR¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined above.

Any alkyl in the abovementioned formula I can be linear or branched.

Y in the formula I is for example ethylene, 1,2- or 1,3-propylene, 1,2-, 1,3- 1,4- or 2,3-butylene, pentamethylene, hexamethylene or 2-methylpentamethylene.

R¹, R², R³, R⁴ and R⁶ in the formula I are each for example methyl, ethyl, propyl, isopropyl, butyl, isobutyl, sec-butyl or tert-butyl.

R¹, R² and R³ are each further for example pentyl, isopentyl, neopentyl, tert-pentyl, hexyl, 2-methylpentyl, heptyl, octyl, 2-ethylhexyl, isooctyl, nonyl, isononyl, decyl or isodecyl.

R¹ and R² are each further for example undecyl, dodecyl, tridecyl, isotridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl or eicosyl. (The terms isooctyl, isononyl, isodecyl and isotridecyl are trivial names due to alcohols obtained by the oxo process (cf. Ullmanns Enzyklopadie der technischen Chemie, 4th edition, volume 7, pages 215-217 and volume 11, pages 435 and 436).)

R³ and R⁴ are each further for example methoxy, ethoxy, propoxy, isopropoxy, butoxy, isobutoxy or secbutoxy.

R³ is further for example pentyloxy, isopentyloxy, neopentyloxy, hexyloxy, heptyloxy, octyloxy, 2-ethylhexyloxy, nonyloxy or decyloxy.

R⁴ is further for example methylthio, ethylthio, propylthio, isopropylthio or butylthio.

R¹ and R² are each further for example benzyl, 1- or 2-phenylethyl. ##STR4##

Preference is given to using in the process according to the invention a substrate on which there are one or more azo dyes of the formula I where

R¹ and R² are each independently of the other alkyl, alkanoyloxyalkyl or alkyloxycarbonylalkyl, each of which may have up to 12 carbon atoms and be substituted by phenyl, C₁ -C₄ -alkylphenyl, C₁ -C₄ -alkoxyphenyl, hydroxyl or cyano, or are each independently of the other unsubstituted or C₁ -C₁₂ -alkyl- or C₁ -C₁₂ -alkoxy-substituted phenyl, unsubstituted or C₁ -C₁₂ -alkyl- or C₁ -C₁₂ -alkoxy-substituted benzyl or a

radical of the formula II ##STR5## where Y is C₂ -C₄ -alkylene,

m is 1, 2, 3 or 4 and

R⁶ is C₁ -C₄ -alkyl or unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl,

R³ is hydrogen, C₁ -C₆ -alkyl, C₁ -C₆ -alkoxy or --NH--CO--R¹, where R¹ is as defined most recently above,

R⁴ is hydrogen, chlorine, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy or phenyl and

R⁵ is cyano or --CO--OR¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined most recently above.

Use is made in the novel process in particular of a substrate on which there are one or more azo dyes of the formula I where

R¹ and R² are each independently of the other C₁ -C₁₂ -alkyl which may be substituted by cyano, phenyl, C₁ -C₄ -alkylphenyl or C₁ -C₄ -alkoxyphenyl, or a radical of the formula III ##STR6## where n is 1, 2, 3 or 4 and

R⁷ is C₁ -C₄ -alkyl or phenyl,

R³ is hydrogen, methyl, methoxy or acetylamino,

R⁴ is chlorine and

R⁵ is cyano or --CO--OR¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined most recently above.

Particularly good results are obtained on using a substrate on which there are one or more azo dyes of the formula I where R² is C₁ -C₆ -alkyl and R¹ is as defined most recently above or is in particular likewise C₁ -C₆ -alkyl.

Particularly favorable results are further obtained on using a substrate on which there are one or more azo dyes of the formula I where R⁵ is cyano or --CO--OR¹, where R¹ is alkyl, alkanoyloxyalkyl or alkyloxycarbonylalkyl, each of which may have up to 12 carbon atoms, or the radical of the abovementioned formula III where n and R⁷ are each as defined above, or R⁷ is in particular C₁ -C₆ -alkyl.

The dyes of the formula I are known from EP-A201,896 or can be obtained by the methods mentioned therein.

Compared with the dyes used in existing processes, the dyes transferred in the process according to the invention are notable in general for improved migration properties in the receiving medium at room temperature, more ready thermal transferability, higher photochemical stability, easier industrial accessibility, better resistance to moisture and chemical substances, higher color strength, better solubility and in particular higher purity of hue.

It is further surprising that the dyes of the formula I are readily transferable despite their relatively high molecular weight.

To prepare the dye substrate required for the novel process, the dyes are incorporated in a suitable organic solvent, for example chlorobenzene, isobutanol, methyl ethyl ketone, methylene chloride, toluene, tetrahydrofuran or a mixture thereof, with one or more binders with or without assistants to give a printing ink. This ink preferably contains the dye in a molecularly dispersed, ie. dissolved, form. The printing ink is applied to the inert substrate by knife coating and dried in air.

Suitable binders are all resins or polymer materials which are soluble in organic solvents and are capable of holding the dye on the inert substrate in an abrasion-resistant bind. Preference is given to binders which, after the printing ink has dried in air, hold the dye in a clear, transparent film without visible crystallization of the dye.

Examples of such binders are cellulose derivatives, for example methylcellulose, ethylcellulose, ethylhydroxyethylcellulose, hydroxypropylcellulose, cellulose acetate or cellulose acetobutyrate, starch, alginates, alkyd resins, vinyl resins, polyvinyl alcohol, polyvinyl acetate, polyvinyl butyrate or polyvinylpyrrolidones. Other possibilities as binders are polymers and copolymers of acrylates or derivatives thereof, such as polyacrylic acid, polymethyl methacrylate or styrene/acrylate copolymers, polyester resins, polyamide resins, polyurethane resins or natural CH resins, such as gum arabic. Further suitable binders are described in DE-A-3,524,519.

Preferred binders are ethylcellulose and ethylhydroxyethylcellulose of medium to small viscosity.

The ratio of binder to dye preferably varies from 5:1 to 1:1.

Possible assistants are release agents as described in EP-A-227,092, EP-A-192,435 and the patent applications cited therein and also particularly organic additives which stop the transfer dye from crystallizing in the course of storage or heating of the inked ribbon, for example cholesterol or vanillin.

Inert substrates are for example tissue, blotting or parchment paper or plastics films of high heat stability, for example uncoated or metal-coated polyester, polyamide or polyimide. The inert substrate may additionally be coated on the side facing the thermal printing head with a lubricant, or slipping, layer in order to prevent adhesion of the thermal printing head to the substrate material. Suitable lubricants are described for example in EP-A-216,483 and EP-A-277,095. The thickness of the dye substrate is in general from 3 to 30 μm, preferably from 5 to 10 μm.

Suitable dye receiver layers are basically all temperature stable plastics layers having an affinity for the dyes to be transferred. Their glass transition temperature should be below 150° C. Examples are modified polycarbonates or polyesters. Suitable recipes for the receiver layer composition are described in detail for example in EP-A-227,094, EP-A-133,012, EP-A-133,011, EP-A-111,004, JP-A-199,997/1986, JP-A-283,595/1986, JP-A-237,694/1986 and JP-A-127,392/1986.

Transfer is effected by means of a thermal printing head which must be heatable to a temperature ≧300° C. for the dye transfer to take place within the time interval t: 0<t<15 msec. On heating, the dye migrates out of the transfer sheet and diffuses into the surface coating of the receiving medium.

Details of the preparation may be found in the Examples, where percentages are by weight, unless otherwise stated.

Transfer of dyes

To be able to test the transfer characteristics of the dyes in a quantitative and simple manner, the thermotransfer was carried out with large hotplates instead of a thermal printing head, with the transfer temperature being varied within the range 70° C.<T<120° C. and the transfer time being set at 2 minutes.

A) General recipe for coating the substrate with dye

1 g of binder was dissolved at from 40° to 50° C. in 8 ml of 8:2 v/v toluene/ethanol. A solution of 0.25 g of dye (and any assistant used) in 5 ml of tetrahydrofuran was added by stirring. The print paste thus obtained was smoothed down with an 80 μm knife on a sheet of polyester film (thickness: 6-10 μm) and dried with a hair dryer.

B) Testing of Thermal transferability

The dyes used were tested in the following manner:

The polyester sheet donor containing the dye under test on the coated front was placed face down on commercial Hitachi Color Video Print Paper (receiver) and pressed down. Donor/receiver were then wrapped in aluminum foil and heated between two hotplates at different temperatures T (within the temperature range 70° C.<T<120° C.). The amount of dye diffusing into the bright plastics layer of the receiver is proportional to the optical density (=absorbance A). The latter was determined photometrically. If the logarithm of the absorbance A of the colored receiver papers measured within the temperature range from 80° to 110° C. is plotted against the corresponding reciprocal absolute temperature, the result is a straight line whose slope gives the activation energy ΔE_(T) for the transfer experiment: ##EQU1##

To complete the characterization, the plots additionally indicate the temperature T*[°C.]at which the absorbance A of the dyed receiver papers attains the value 2.

The dyes mentioned in the Tables below were processed according to A), and the resulting dye-coated substrates were tested in respect of their transfer characteristics by B). The Tables list in each case the thermotransfer parameters T* and ΔE_(T), the absorption maximum of the dyes λ_(max) (measured in methylene chloride), the binders used and the assistants.

The abbreviations have the following meanings:

B=binder (EC=ethylcellulose, EHEC=ethylhydroxyethylcellulose, MIX=mixture of polyvinyl butyrate and ethylcellulose in a weight ratio of 2:1)

D=dye

AUX=auxiliary (chol=cholesterol)

                                      TABLE 1                                      __________________________________________________________________________      ##STR7##                                                                       No.pleam-Ex-                                                                      A.sup.1  A.sup.2        A.sup.3        λ.sub.max [nm]                                                             B   AUX                                                                                T* [°C.]                                                                   ##STR8##              __________________________________________________________________________      1 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.2 H.sub.5                                                                               645                                                                               EC  --  114                                                                               13                      2 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.2 H.sub.5                                                                               645                                                                               EC  0.19 g                                                                             101                                                                               18                                                                      of chol                        3 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.4 H.sub.9                                                                               648                                                                               EC  --  113                                                                               12                      4 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.2 H.sub.4OC.sub.2 H.sub.4OCH.sub.3                                                      650                                                                               EC  --  116                                                                               14                      5 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.2 H.sub.4OC.sub.2 H.sub.4OC.sub.4                                        H.sub.9        650                                                                               EHEC                                                                               --  100                                                                               16                      6 CH.sub.3 C.sub.3 H.sub.7                                                                               C(CH.sub.3).sub.3                                                                             633                                                                               EC  0.38 g                                                                             102                                                                               27                                                                      of chol                        7 CH.sub.3 CH(CH.sub.3).sub.2                                                                            C.sub.4 H.sub.9                                                                               640                                                                               EC  --  102                                                                               24                      8 CH.sub.3 C.sub.3 H.sub.7                                                                               C.sub.4 H.sub.9                                                                               643                                                                               EC  --  106                                                                               21                      9 C.sub.4 H.sub.9                                                                         C.sub.6 H.sub.13                                                                              CH.sub.3       649                                                                               EC  --  109                                                                               18                     10 C.sub.4 H.sub.9                                                                         C.sub.6 H.sub.13                                                                              C(CH.sub.3).sub.3                                                                             641                                                                               EC  --  111                                                                               20                     11 C.sub.4 H.sub.9                                                                         C.sub.6 H.sub.13                                                                              C.sub.2 H.sub.5                                                                               648                                                                               EC  --  115                                                                               18                     12 C.sub.4 H.sub.9                                                                         C.sub.6 H.sub.13                                                                              C.sub.4 H.sub.9                                                                               650                                                                               EC  --  114                                                                               15                     13 C.sub.2 H.sub. 5                                                                         ##STR9##      C.sub.4 H.sub.9                                                                               644                                                                               EC  --  112                                                                               19                     14 C.sub.2 H.sub.5                                                                          ##STR10##     C.sub.4 H.sub.9                                                                               644                                                                               EHEC                                                                               --  105                                                                               15                     15 C.sub.2 H.sub.5                                                                         C.sub.8 H.sub.17                                                                              C.sub.2 H.sub.5                                                                               648                                                                               EC  --  113                                                                               23                     16 C.sub.2 H.sub.5                                                                         C.sub.8 H.sub.17                                                                              C.sub.4 H.sub.9                                                                               645                                                                               EC  --  107                                                                               18                     17 C.sub.2 H.sub.5                                                                         C.sub.8 H.sub.17                                                                              CH.sub.3       649                                                                               EC  --  106                                                                               20                     18 C.sub.2 H.sub.5                                                                         C.sub.6 H.sub.13                                                                              C.sub.4 H.sub.9                                                                               646                                                                               EC  --  105                                                                               21                     19 C.sub.4 H.sub.9                                                                          ##STR11##     C.sub.2 H.sub.5                                                                               650                                                                               EC  --  113                                                                               14                     20 C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.4OC.sub.4 H.sub.9                                                               C.sub.2 H.sub.5                                                                               637                                                                               EC  --  104                                                                               17                     21 C.sub.4 H.sub.9                                                                         C.sub.2 H.sub.4OC.sub.4 H.sub.9                                                               C.sub.2 H.sub.5                                                                               640                                                                               EC  --  111                                                                               10                     22 C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.4OC.sub.2 H.sub.4OCH.sub.3                                                      C.sub.2 H.sub.5                                                                               639                                                                               EC  --  107                                                                               16                     23 C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.4OC.sub.2 H.sub.4OC.sub.4 H.sub.9                                               C.sub.2 H.sub.5                                                                               636                                                                               EC  --  104                                                                               12                     24 C.sub.4 H.sub.9                                                                         C.sub.2 H.sub.4OC.sub.2 H.sub.4OC.sub.4 H.sub.9                                               C.sub.2 H.sub.5                                                                               639                                                                               EC  --  106                                                                               11                     25 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               CH.sub.3       645                                                                               EC  --  112                                                                               12                     26 C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                         C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                               C.sub.4 H.sub.9                                                                               626                                                                               EC  --  106                                                                               13                     27 C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                         C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                               CH.sub.3OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                                      636                                                                               EC  --  109                                                                                9                     28 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.6 H.sub.5OC.sub.2 H.sub.4                                                               652                                                                               EC  --  130                                                                               13                     29 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                               647                                                                               EC  --  109                                                                               19                     30 C.sub.4 H.sub.9                                                                         C.sub.4 H.sub.9                                                                               C.sub.6 H.sub.5OC.sub.2 H.sub.4OC.sub.2                                        H.sub.4        649                                                                               EC  --  118                                                                               17                     31 C.sub.4 H.sub.9                                                                         CH(CH.sub.3).sub.2                                                                            C.sub.4 H.sub.9                                                                               647                                                                               MIX --  100                                                                               12                     32 C.sub.3 H.sub.7                                                                         CH(CH.sub.3).sub.2                                                                            C.sub.4 H.sub.9                                                                               647                                                                               MIX --  102                                                                               13                     33 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.5                                                                      C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2                                        H.sub.4        648                                                                               EC  --  111                                                                               22                     34 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.5                                                                      CH.sub.3OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                                      649                                                                               EC  --  118                                                                               21                     35 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.7                                                                      C.sub.6 H.sub.5OC.sub.2 H.sub.4                                                               649                                                                               EC  --  124                                                                               15                     36 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.7                                                                      C.sub.6 H.sub.5OC.sub.2 H.sub.4OC.sub.2                                        H.sub.4        649                                                                               EC  --  121                                                                               15                     37 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.7                                                                      C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2                                        H.sub.4        648                                                                               EC  --  113                                                                               18                     38 C.sub.2 H.sub.5                                                                         CH.sub.3(CH.sub.2).sub.7                                                                      C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                               639                                                                               EC  --  110                                                                               14                     39 C.sub.4 H.sub.9                                                                          ##STR12##     C.sub.2 H.sub.5                                                                               649                                                                               EC  --  113                                                                               21                     40 C.sub.4 H.sub.9                                                                         C.sub.6 H.sub.5OC.sub.2 H.sub.4                                                               C.sub.4 H.sub.9                                                                               631                                                                               EC  --  133                                                                               16                     __________________________________________________________________________

                                      TABLE 2                                      __________________________________________________________________________      ##STR13##                                                                      No.Example                                                                          A.sup.1                                                                           A.sup.2                                                                              A.sup.3        λ.sub.max [nm]                                                               B  AUX                                                                                T*[°C.]                                                                     ##STR14##                        __________________________________________________________________________     41   C.sub.4 H.sub.9                                                                   C.sub.4 H.sub.9                                                                      CH.sub.3(CH.sub.2).sub.6                                                                      635  EC --  115 10                                42   C.sub.4 H.sub.9                                                                   CH.sub.3 (CH.sub.2).sub.5                                                            CH.sub.3(CH.sub.2).sub.6                                                                      637  EC --  126 17                                43   C.sub.4 H.sub.9                                                                   CH.sub.3 (CH.sub.2).sub.5                                                            C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                               649  EC --  111 11                                44   C.sub.4 H.sub.9                                                                   C.sub.4 H.sub.9                                                                      C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                               649  EC --  121 11                                __________________________________________________________________________

                                      TABLE 3                                      __________________________________________________________________________      ##STR15##                                                                      No.Example                                                                          A.sup.1                                                                           A.sup.2          A.sup.3                                                                           λ.sub.max [nm]                                                               B  AUX    T*[°C.]                                                                     ##STR16##                      __________________________________________________________________________     45   C.sub.4 H.sub.9                                                                   C.sub.4 H.sub.9  H  672  EC 0.19 g of chol                                                                        100 18                              46   C.sub.4 H.sub.9                                                                    ##STR17##       H  674  EC --     105 20                              47   C.sub.2 H.sub.5                                                                    ##STR18##       H  651  EC --     110 12                              48   C.sub.4 H.sub.9                                                                   C.sub.4 H.sub.9  CH.sub.3                                                                          683  MIX                                                                               --     107 14                              __________________________________________________________________________

    TABLE 4       ##STR19##                  Example No. A.sup.1 A.sup.2 A.sup.3 A.sup.4 λ.sub.max      [nm] B AUX T*[°C.]       ##STR20##        49 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.3 H.sub.7CONH 6      49 EC -- 126 22 50 C.sub.2 H.sub.5 C.sub.2 H.sub.5 C.sub.4       H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4 C.sub.4 H.sub.9NHCONH 645 EC --       120 14 51 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.4 H.sub.9OC.sub.2      H.sub.4OC.sub.2 H.sub.4 C.sub.2 H.sub.5CONH 650 EC -- 129 10  52 C.sub.2      H.sub.5 C.sub.2 H.sub.5 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4       ##STR21##       667 EC -- 140 13  53 C.sub.4 H.sub.9 CH.sub.3COOC.sub.2 H.sub.4 C.sub.4      H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4 CH.sub.3CONH 667 EC -- 145  7 54      C.sub.6 H.sub.5CH.sub.2 C.sub.2 H.sub.5 C.sub.4 H.sub.9OC.sub.2       H.sub.4OC.sub.2 H.sub.4 CH.sub.3CONH 635 EC -- 128 12 55 C.sub.2      H.sub.5 CH.sub.3COOC.sub.2 H.sub.4 C.sub.4 H.sub.9 C.sub.6 H.sub.5CONH      647 MIX -- 119 18 56 C.sub.4 H.sub.9 NCC.sub.2 H.sub.4 C.sub.4 H.sub.9      CH.sub.3CONH 619 MIX -- 122 19 57 C.sub.4 H.sub.9 CH.sub.3COOC.sub.2      H.sub.4 C.sub.4 H.sub.9 CH.sub.3CONH 631 MIX -- 111 16 58 C.sub.6        C      H.sub.5H.sub.2 CH.sub.3COOCH.sub.2 C.sub.4 H.sub.9OC.sub.2       H.sub.4OC.sub.2       H.sub.4 CH.sub.3CONH 614 MIX -- 116 10 59 CH.sub.3COOC.sub.4 H.sub.8      CH.sub.3COOC.sub.4 H.sub.8 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2      H.sub.4 CH.sub.3CONH 640 EC -- 115 14 60 C.sub.2 H.sub.5 H.sub.3      COOCC.sub.2 H.sub.4 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4      CH.sub.3CONH 632 EC -- 130 10 61 C.sub.2 H.sub.5 C.sub.4       H.sub.9OOCC.sub.2 H.sub.4 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2      H.sub.4 CH.sub.3CONH 625 EC -- 131  9 62 CH.sub.3COOC.sub.2 H.sub.4      CH.sub.3COOC.sub.2 H.sub.4 C.sub.4 H.sub.9 CH.sub.3 617 EC -- 114 11  63      C.sub.2       H.sub.5      ##STR22##       C.sub.4 H.sub.9 CH.sub.3 631 MIX -- 106 13  64 C.sub.4 H.sub.9 C.sub.4      H.sub.9 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4 CH.sub.3 661 EC      -- 113 16 65 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.4 H.sub.9OC.sub.2      H.sub.4 CH.sub.3 658 EC -- 116 13 66 (CH.sub.3).sub.2 CH HOC.sub.2      H.sub.4 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4 CH.sub.3 636 EC      -- 129  8 67 C.sub.2 H.sub.5 ClC.sub.2 H.sub.4 C.sub.4 H.sub.9OC.sub.2      H.sub.4OC.sub.2 H.sub.4 CH.sub.3 629 EC -- 124 12 68 C.sub.4 H.sub.9      C.sub.4 H.sub.9 C.sub.4 H.sub.9 CH.sub.3 659 EC -- 127 10 69 C.sub.4      H.sub.9 C.sub.4 H.sub.9 C.sub.2 H.sub.5 CH.sub.3 658 MIX -- 104 18 70      C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.3 H.sub.7 CH.sub.3 656 MIX -- 99      15 71 C.sub.4 H.sub.9 C.sub.4 H.sub.9 CH.sub.3 CH.sub.3 660 MIX -- 112      16 72 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.4 H.sub.9OC.sub.2       H.sub.4OC.sub.2 H.sub.4 OCH.sub.3 656 MIX -- 116 12 73 C.sub.4 H.sub.9      C.sub.4 H.sub.9 C.sub.4 H.sub.9OC.sub.2 H.sub.4 OCH.sub.3 656 EC -- 107      11 74 C.sub.4 H.sub.9 C.sub.4 H.sub.9 C.sub.4 H.sub.9OC.sub.2       H.sub.4OC.sub.2 H.sub.4 OCH.sub.3 655 EC -- 113 13 75 C.sub.4 H.sub.9      C.sub.4 H.sub.9 C.sub.4 H.sub.9 OCH.sub.3 655 EC -- 114 14 76 C.sub.2      H.sub.5 C.sub.2 H.sub.5 C.sub.4 H.sub.9 OCH(CH.sub.3).sub.2 636 MIX --      106 14  77 C.sub.2 H.sub.5 C.sub.2 H.sub.5 C.sub.4       H.sub.9      ##STR23##       645 MIX -- 103 15      ##STR24##

                                      TABLE 5                                      __________________________________________________________________________     Ex-                                                                            am-                                                                            ple                                                                            No.                                                                               A.sup.1       A.sup.2        A.sup.3        A.sup.4  A.sup.5                __________________________________________________________________________     78 C.sub.3 H.sub.7                                                                              C.sub.3 H.sub.7                                                                               C.sub.4 H.sub.9                                                                               H        H                      79 C.sub.4 H.sub.9                                                                              C.sub.6 H.sub.13                                                                              C.sub.2 H.sub.5                                                                               H        CH.sub.3               80 C.sub.4 H.sub.9                                                                              C.sub.4 H.sub.9                                                                               CH.sub.3       CH.sub.3CONH                                                                            CH.sub.2 H.sub.5O                                                              1                      81 C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                              C.sub.4 H.sub.9                                                                               C.sub.4 H.sub.9                                                                               CH.sub.3 CH.sub.3               82 C.sub.4 H.sub.9                                                                              CH.sub.3OC.sub.2 H.sub.4                                                                      C.sub.3 H.sub.7                                                                               CH.sub.3O                                                                               C.sub.6 H.sub.5        83 C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                              C.sub.2 H.sub.5                                                                               C.sub.4 H.sub.9                                                                               H                               84                                                                                 ##STR25##    C.sub.4 H.sub.9                                                                               CH.sub.3       CH.sub.3 CH.sub.3               85 C.sub.2 H.sub.5                                                                              C.sub. 6 H.sub.5OC.sub.2 H.sub.4OC.sub.2 H.sub.4                                              C.sub.4 H.sub.9                                                                               CH.sub.3CONH                                                                            CH.sub.3               86 C.sub.3 H.sub.7                                                                              C.sub.4 H.sub.9                                                                               C.sub.4 H.sub.9OC.sub.2 H.sub.4                                                               C.sub.2 H.sub.5                                                                         CH.sub.3               87 C.sub.4 H.sub.9                                                                              C.sub.4 H.sub.9                                                                               C.sub.4 H.sub.9OC.sub.2 H.sub.4OC.sub.2                                        H.sub.4        CH.sub.3 C.sub.2 H.sub.5        88 C.sub.4 H.sub.9                                                                              C.sub.2 H.sub.5                                                                               C.sub.6 H.sub.5OC.sub.2 H.sub.4OC.sub.3                                        H.sub.6        C.sub.2 H.sub.5                                                                         C.sub.2 H.sub.5O       89 C.sub.10 H.sub.21                                                                            C.sub.2 H.sub.5                                                                               CH.sub.3       CH.sub.3CONH                                                                            H                      __________________________________________________________________________ 

We claim:
 1. A process for transferring azo dyes from a substrate to a plastic-coated paper by diffusion with the aid of a thermal printing head, which comprises using a substrate on which there are one or more azo dyes of the formula I ##STR26## where R¹ and R² are identical or different and each is, independently of the other: alkyl, alkanoyloxyalkyl, alkoxycarbonyloxyalkyl or alkoxycarbonylalkyl, each group having 1 to 20 carbon atoms or R¹ and R² are independently, one of the above-mentioned groups either unsubstituted or substituted by phenyl, C₁ -C₄ -alkylphenyl, C₁ -C₄ -alkoxyphenyl, benzyloxy, C₁ -C₄ -alkylbenzyloxy, C₁ -C₄ -alkoxybenzyloxy, halogen, hydroxyl or cyano, or are each independently of the other hydrogen, unsubstituted or C₁ -C₂₀ -alkyl-, C₁ -C₂₀ -alkoxy- or halogen-substituted phenyl, unsubstituted or C₁ -C₂₀ -alkyl-, C₁ -C₂₀ -alkoxy- or halogen-substituted benzyl, unsubstituted or C₁ -C₂₀ -alkyl-, C₁ -C₂₀ -alkoxy- or halogen-substituted benzyl or formula II

    [--Y--O .sub.m --R.sup.6

where Y is C₂ -C₆ -alkylene, m is 1, 2, 3, 4, 5 or 6 and R₆ is C₁ -C₄ -alkyl or unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl, or each is a radical of the formula II R³ is hydrogen, C₁ -C₁₀ -alkyl, C₁ -C₁₀ -alkoxy or --NH--CO--R¹, where R¹ is as defined above, R⁴ is hydrogen, chlorine, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, C₁ -C₄ -alkylthio or unsubstituted or C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy- or halogen-substituted phenyl and R⁵ is cyano or --CO--R¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined above provided that when R⁵ is CN one of R¹ and R² is the radical of formula II.
 2. A process as claimed in claim 1, wherein on the substrate used there are one or more azo dyes of the formula I whereR¹ R² are each independently of the other alkyl, alkanoyloxyalkyl or alkyloxycarbonylalkyl, each group having 1 to 20 carbon atoms or are the above-mentioned groups substituted by phenyl, C₁ -C₄ -alkylphenyl, C₁ -C₄ -alkoxyphenyl, hydroxyl or cyano, or are each independently of the other unsubstituted or C₁ -C₁₂ -alkyl-, C₁ -C₁₂ -alkoxy-substituted phenyl, unsubstituted or C₁ -C₁₂ -alkyl-, C₁ -C₁₂ -alkoxy-substituted benzyl or a radical of the formula II

    [--Y--O].sub.m --R.sup.6                                   (II)

where Y is C₂ -C₄ -alkylene, m is 1, 2, 3, or 4 and R⁶ is C₁ -C₄ -alkyl or unsubstituted or C₁ -C₄ -alkyl- or C₁ -C₄ -alkoxy-substituted phenyl, R³ is hydrogen, C₁ -C₆ alkyl, C₁ -C₆ -alkoxy or --NH--CO--R¹, where R¹ is as defined above, R⁴ is hydrogen, chlorine, C₁ -C₄ -alkyl, C₁ -C₄ -alkoxy, or phenyl and R⁵ is cyano or --CO--R¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined above.
 3. A process as claimed in claim 1, wherein on the substrate used there are one or more azo dyes of the formula I whereR¹ and R² are each independently of the other C₁ - C₁₂ -alkyl or C₁ -C₁₂ -alkyl substituted by cyano, phenyl, C₁ -C₄ -alkylphenyl or C₁ -C₄ -alkoxyphenyl, or a radical of the formula III

    [--CH.sub.2 --CH.sub.2 --O].sub.n --R.sup.7                (III)

where n is 1, 2, 3, or 4 and R⁷ is C₁ -C₄ -alkyl or phenyl, R³ is hydrogen, methyl, methoxy or acetylamino, R⁴ is chlorine and R⁵ is cyano or --CO--R¹, --CO--NHR¹ or --CO--NR¹ R², where R¹ and R² are each as defined above. 